The relevance of DNA- adduct formation from endogenous chemicals and their potential role in the progression to cancer will be examined. Methodology will be developed for the structural and quantitative analysis of DNA-adduct derived from endogenous carcinogens. This will eventually allow a correlation to be made between DNA-adduct structures and their potential role in carcinogenesis. Liquid chromatography - electrospray mass spectrometry will be employed for analysis of modified nucleosides and nucleotides. This methodology will then be extended to analysis of oligonucleotides. To facilitate structural characterization and quantitation of DNA adducts, E. Coli with [13C][15N] DNA will be prepared. Stable isotope labeled adducts incorporated into DNA will be quantified by chemical reaction interface mass spectrometry. Finally endogenous DNA-adducts from in vivo models of lipid peroxidation and human breast cancer tissue samples will be characterized and quantified. This will allow testing of the hypothesis that endogenous DNA adducts provide a marker of DNA damage that arises from endogenous pathways of carcinogenesis.